In a casing used for a cylinder of a turbine or a compressor, a dividable structure is generally adopted. Such a casing is presented with a challenge that the outward gas leakage must be suppressed at the flange surface. Particularly, if helium gas is used as working gas, not only the leakage tends to occur much easier than other gas, such as steam, but also it is more expensive. Therefore, in a fluid machine (turbine or compressor) using high-pressure helium gas as working gas, there has been a demand for suppressing the leakage of the working gas more effectively. Therefore, in a known casing, various types of sealing structures are used for the flange section.
One of the known casings (a sealing structure for the flange section of a pressure container) is disclosed in Patent Document 1. In flanges of a pressure container of the known casing for enclosing cover gas, including sodium or sodium mist, a ring element, having an I-shaped cross section, is provided onto the entire circumference of the flange. In this manner, the ring element protrudes inwardly from a bolt attaching portion of one of the flanges, which are joined together by flange bolts, into an inter-space between the flanges. At the same time, the other flange includes a ring element, having a J-shaped cross section, on the entire circumference thereof along the former ring element. The edges of these ring elements are engaged and welded together to form a U-shaped sealing element for sealing the cover gas, including the sodium or the sodium mist, inside the container.
[Patent Document 1] Japanese Patent Application Laid Open No. S55-17712